A chassis of a swivel chair, also named as a tray of a swivel chair, is an important part arranged under a seating washer of the swivel chair, and the lift of the seating washer as well as the tilt angle of a backrest is adjusted thereby.
In the prior art, the chassis of the swivel chair usually consists of many parts such as an upper tray, a lower trimming beam, a rotating shaft and a spring device, wherein after an upper turn plate is fixed with the back side of a seat of the swivel chair, the swivel chair can be properly tilted around the rotating shaft and can reset automatically, so that users feel comfortable. For example, the Chinese patent discloses a tray (patent number is: 02287885.8), mainly comprising a base plate, a movable seat, a tapered pipe and an adjusting device, wherein the movable seat is movably connected onto the base plate, and the middle of the movable seat is connected with the tapped pipe of an air pressure stick, and the movable seat is welded onto the movable seat with the tapped pipe by the tapped pipe fixing plate; the adjusting device comprises an adjusting lever, an adjusting plate, a torsion spring a and a torsion spring a fixing plate, wherein the adjusting lever is inserted into the movable seat, the adjusting plate is fixedly connected onto one end of the adjusting lever, which is inserted into the movable seat, one side of the adjusting plate is contacted with the air pressure stick, and the other side thereof is connected with the torsion spring a; a rotation stopping sheet of the adjusting plate is arranged on the other side of the adjusting plate.
The adjusting device of the tray of the swivel chair is completely adjusted by the torsion spring, while for the users with different weight, the needed force of the torsion spring should be different, so that the product is not very good in universality. Aiming at the problem, the Chinese patent with the patent number of ‘201020264417.6’ discloses a rolling shaft-adjusted tray of a swivel chair, wherein the gravity applied onto the surface of the chair is conducted into the reset force of the backrest, so that the swivel chair can be basically used for the users with different weight without being adjusted. However, when users sit on the chair provided with the tray and backwards tilt, as a part of the human gravity is supported by the backrest and the proportion is gradually increased, the gravity applied onto the surface of the seat is gradually reduced, and the reset force conduced by the gravity to the backseat is reduced along therewith, so that the reset force of the backseat is insufficient when the tilt angle is maximum, and the reset force excessively depends on the elastic recovery of an elastic reset device, therefore, the chair in the prior is limited in the target people scope, the users with light weight are hard to tilt, or the users with heavy weight are hard to reset to get up after titling, thus the most reasonable matched reset force can not be achieved.